Taxonomy & naming
Characidium laterale was described by the Belgian-British ichthyologist George Albert Boulenger in 1895. It sits in the genus Characidium within the family Crenuchidae — the South American darters and sailfin characins — a family placed in the order Characiformes alongside the tetras, piranhas and pacus but ecologically closer to a bottom-dwelling darter or goby than to an open-water tetra. The Catalog of Fishes (Eschmeyer, California Academy of Sciences) is the governing authority for the valid name and combination used here.
Characidium is a large, taxonomically active genus of small, superficially similar barred or blotched darters, and species-level identification in the hobby trade is unreliable without close examination or locality data; fish sold simply as "Characidium sp." or under a trade name may not match the species pictured. C. laterale is recorded from the Paraná River basin and from the Potaro and Mazaruni Rivers in Guyana — a distribution pattern consistent with the historical dispersal of Characidium lineages from the Amazon paleobasin into southeastern South America documented in the biogeographic literature.
Morphology
Like other Characidium, C. laterale has an elongated, cylindrical, faintly compressed body built for hovering and short bursts rather than sustained swimming, with a flattened lower profile that lets it perch stably on stone and sand. FishBase records a maximum size of just 1.5 in standard length, making it one of the smaller members of an already small-bodied genus. Colouration typical of the group includes a dark lateral stripe or series of blotches running the length of the body, a pale to silvery ground colour, and subtle barring that breaks up its outline against mixed substrate — camouflage suited to a fish that relies on staying still and unnoticed between darts rather than on speed alone.
No reliable external sexual dimorphism has been documented for this species in the sources reviewed here; as with many small characins, mature females may appear slightly deeper-bodied when gravid, but this is not a confirmed, consistent field mark.
Habitat
Characidium laterale is a freshwater, benthopelagic species of tropical South American streams and rivers, recorded from the Paraná River basin and from the Potaro and Mazaruni Rivers in Guyana. Both drainages carry clear-to-tea-coloured, flowing water over stone, gravel and sand substrates, and darter characins in general are strongly associated with well-oxygenated, moving water rather than still backwaters — the perching, dart-and-rest behaviour that gives the group its common name is a foraging strategy suited to a current-swept streambed, not a quiet pool.
Hobby accounts of darter characins as a group describe soft, mildly acidic water, roughly pH 6.5–7.0, and a moderate, subtropical-leaning temperature range of about 72–79 °F — cooler than the warm Amazonian lowland conditions many characins tolerate, consistent with the Paraná basin population running through a more temperate part of South America than the equatorial Amazon.
Feeding
Characidium laterale is a micro-predator, not a grazer or generalist scavenger. In the wild it almost certainly takes small aquatic invertebrates, insect larvae and other micro-crustaceans picked directly off the substrate between darts, in keeping with the diet documented for darter characins generally. In the aquarium this translates to a fish that often ignores dry flake outright and needs to be offered small live or frozen foods — bloodworm, brine shrimp, Daphnia and Cyclops are all specifically recommended for the group.
Because it forages at the substrate rather than in midwater, food needs to reach the bottom before faster or more aggressive tankmates take it; keepers report best results feeding directly over open sand or gravel patches where the fish naturally perches, rather than relying on food drifting down through the water column.
Mating
Documented courtship detail specific to Characidium laterale is sparse. What is recorded for darter characins as a group is that spawning is associated with soft, acidic water and the presence of fine-leaved plants or spawning mops, suggesting a trigger tied to water softness and cover availability rather than an elaborate courtship display. No reliable external sexual dimorphism is documented for this species, so hobbyists pairing fish for breeding typically rely on behavioural cues and relative body fullness in ripe females rather than colour or fin differences.
Breeding
Characidium in general are egg-scatterers over the substrate, without the cave- or leaf-guarding male parental care documented in their Crenuchidae relatives Crenuchus and Poecilocharax. Practical Fishkeeping's darter-characin care coverage describes natural spawning taking place in well-maintained aquaria given soft, acidic water and fine-leaved plants such as Java moss or spawning mops for the adhesive eggs to catch on, but does not describe any nest defence or brooding behaviour for C. laterale specifically. Treat this as an egg-scattering species with no meaningful parental care; hobbyist reports of successful breeding exist, but detailed clutch size, incubation time and fry-rearing specifics are not established in the sources available here — data sparse beyond the general spawning conditions above.
In the aquarium
Characidium laterale needs current more than it needs space: Practical Fishkeeping recommends well-oxygenated water with moderate to strong flow, achievable with an appropriately sized filter outlet or powerhead, in a tank of around 20 US gallons (roughly 20 US gal) upward for a small group. Furnish with smooth stones and driftwood but leave open areas of bare sand or fine gravel — the fish needs clear substrate to perch on and dart across, and a tank crowded wall-to-wall with plants or decor works against its natural behaviour.
Water should be kept soft and only mildly acidic to neutral, around pH 6.5–7.0, at a moderate 72–79 °F — cooler than many tropical characin recommendations, reflecting the more temperate Paraná basin part of its range. As a small, non-aggressive micro-predator it is best kept in a species or quiet community tank with similarly gentle, appropriately sized tankmates; boisterous or fast midwater fish will simply out-compete it for food, since it takes small live or frozen items from the substrate rather than flake from the surface.
Conservation
The IUCN Red List assesses Characidium laterale as Least Concern, an assessment reflected in FishBase's summary for the species (assessment dated 24 February 2020). Its range spans two separate drainages — the Paraná basin and the Potaro/Mazaruni Rivers of Guyana — and there is no indication in the sources reviewed here of significant population decline or a concentrated single-site threat. As with most small, non-commercial characins, the aquarium trade in this species is likely limited relative to demand for larger or more colourful characins, and specific data on collection pressure or trade volume is not available.